Most quantization related schemes adjust quantization parameters to control picture quality and bit allocation. For example, a block based signal compression system employs quantization of codewords or transform coefficients and includes circuitry for adaptively controlling the quantization. Adaptivity of quantization may be a function of coding cost or bandwidth. Coding cost may be determined on a macroblock basis but averaged over a window of macroblocks centered on a macroblock currently being quantized. Other block or macroblock motion attributes can also be used to modify the quantizing function. However, these encoding schemes do not address the problems associated with quantization threshold or rounding.
For example, in existing video encoding systems, quantization offset parameters are typically pre-fixed constants, such as ½, ⅓, and ⅙, etc. In the H.264 reference software encoder, which is considered as a collection of many state-of-art video encoding tools, the relative quantization rounding offset is set to ⅓ for all Intra modes, while the rounding offset is set to ⅙ for all Inter modes.
These and other picture encoding schemes evaluate data quantity from stored picture data and detect inter-picture correlation. Picture data compression is then adaptively selected based upon the evaluated value of the information quantity and the inter-picture correlation information. The basic quantization step is then adaptively adjusted according to bit allocation and picture correlation. However, problems associated with quantization rounding are not taken into account.
The present invention addresses this and other problems associated with the prior art.